The present invention relates to a compound of the formula 
This compound is an adenosine receptor ligand useful in the control or prevention of illnesses modulated by the adenosine system, such as, for example, Alzheimer""s disease and Parkinson""s disease.
Adenosine modulates a wide range of physiological functions by interacting with specific cell surface receptors. The potential of adenosine receptors as drug targets was first reviewed in 1982. Adenosine is related both structurally and metabolically to the bioactive nucleotides adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and cyclic adenosine monophosphate (cAMP); to the biochemical methylating agent S-adenosyl-L-methione (SAM); and structurally to the coenzymes NAD, FAD and coenzyme A; and to RNA. Together adenosine and these related compounds are important in the regulation of many aspects of cellular metabolism and in the modulation of different central nervous system activities.
The receptors for adenosine have been classified as A1, A2A, A2B and A3 receptors, belonging to the family of G protein-coupled receptors. Activation of adenosine receptors by adenosine initiates signal transduction mechanism. These mechanisms are dependent on the receptor associated G protein. Each of the adenosine receptor subtypes has been classically characterized by the adenylate cyclase effector system, which utilizes cAMP as a second messenger. The A1 and A3 receptors, coupled with Gi proteins inhibit adenylate cyclase, leading to a decrease in cellular cAMP levels, while A2A and A2B receptors couple to G, proteins and activate adenylate cyclase, leading to an increase in cellular cAMP levels. It is known that the A1 receptor system include the activation of phospholipase C and modulation of both potassium and calcium ion channels. The A3 subtype, in addition to its association with adenylate cyclase, also stimulates phospholipase C and so activates calcium ion channels.
The A1 receptor (326-328 amino acids) was cloned from various species (canine, human, rat, dog, chick, bovine, guinea-pig) with 90-95% sequence identify among the mammalian species. The A2A receptor (409-412 amino acids) was cloned from canine, rat, human, guinea pig and mouse. The A2B receptor (332 amino acids) was cloned from human and mouse with 45% homology of human A2B with human A1 and A2A receptors. The A3 receptor (317-320 amino acids) was cloned from human, rat, dog, rabbit and sheep.
The A1 and A2A receptor subtypes are proposed to play complementary roles in adenosine""s regulation of the energy supply. Adenosine, which is a metabolic product of ATP, diffuses from the cell and acts locally to activate adenosine receptors to decrease the oxygen demand (A1) or increase the oxygen supply (A2A) and so reinstate the balance of energy supply versus demand within the tissue. The actions of both subtypes is to increase the amount of available oxygen to tissue and to protect cells against damage caused by a short-term imbalance of oxygen. One of the important functions of endogenous adenosine is preventing damage during traumas such as hypoxia, ischaemia, hypotension and seizure activity.
Furthermore, it is known that the binding of the adenosine receptor agonist to mast cells expressing the rat A3 receptor resulted in increased inositol triphosphate and intracellular calcium concentrations, which potentiated antigen induced secretion of inflammatory mediators. Therefore, the A3 receptor plays a role in mediating asthmatic attacks and other allergic responses.
Adenosine is also a neuromodulator, possessing global importance in the modulation of molecular mechanisms underlying many aspects of physiological brain function by mediating central inhibitory effects. An increase in neurotransmitter release follows traumas such as hypoxia, ischaemia and seizures. These neurotransmitters are ultimately responsible for neural degeneration and neural death, which causes brain damage or death of the individual. The adenosine A1 agonists which mimic the central inhibitory effects of adenosine may therefore be useful as neuroprotective agents. Adenosine has been proposed as an endogenous anticonvulsant agent, inhibiting glutamate release from excitory neurons and inhibiting neuronal firing. Adenosine agonists therefore may be used as antiepileptic agents. Adenosine antagonists stimulate the activity of the CNS and have proven to be effective as cognition enhancers. Selective A2a-antagonists have therapeutic potential in the treatment of various forms of dementia, for example in Alzheimer""s disease and are useful as neuroprotective agents. Adenosine A2-receptor antagonists inhibit the release of dopamine from central synaptic terminals and reduce locomotor activity and consequently improve Parkinsonian symptoms. The central activities of adenosine are also implicated in the molecular mechanism underlying sedation, hypnosis, schizophrenia, anxiety, pain, respiration, depression and substance abuse. Drugs acting at adenosine receptors therefore have also therapeutic potential as sedatives, muscle relaxants, antipsychotics, anxiolytics, analgesics, respiratory stimulants and antidepressants.
An important role for adenosine in the cardiovascular system is as a cardioprotective agent. Levels of endogenous adenosine increase in response to ischaemia and hypoxia, and protect cardiac tissue during and after trauma (preconditioning). Adenosine agonists thus have potential as cardioprotective agents.
Adenosine modulates many aspects of renal function, including renin release, glomerular filtration rate and renal blood flow. Compounds, which antagonize the renal affects of adenosine, have potential as renal protective agents. Furthermore, adenosine A3 and/or A2B antagonists may be useful in the treatment of asthma and other allergic responses.
Numerous documents describe the current knowledge on adenosine receptors, for example the following publications:
Bioorganic and Medicinal Chemistry, 6, (1998), 619-641,
Bioorganic and Medicinal Chemistry, 6, (1998), 707-719,
J. Med. Chem., (1998), 41, 2835-2845,
J. Med. Chem., (1998), 41, 3186-3201,
J. Med. Chem., (1998), 41, 2126-2133,
J. Med. Chem., (1999), 42, 706-721,
J. Med. Chem., (1996), 39, 1164-1171,
Arch. Pharm. Med. Chem., (1999), 332, 39-41.
The present invention is a compound of formula 
wherein
R1 is xe2x80x94NRxe2x80x2Rxe2x80x3, wherein Rxe2x80x2 and Rxe2x80x3 are independently selected from the group consisting of lower alkyl, xe2x80x94(CH2)nxe2x80x94C(O)NRaRb, xe2x80x94(CH2)n-heteroaryl, xe2x80x94(CH2)n-aryl, xe2x80x94(CH2)nxe2x80x94CN, xe2x80x94(CH2)nxe2x80x94O-lower alkyl or xe2x80x94(CH2)n-cycloalkyl, or Rxe2x80x2 and Rxe2x80x3 form together with the N-atom a five or six-membered non-aromatic ring, containing no or one additional heteroatom selected from the group O and S, said ring being unsubstituted or substituted by one or two substituents, selected from the group consisting of lower alkyl, xe2x80x94C(O)NRaRb or xe2x80x94(CH2)nxe2x80x94O-lower alkyl and RaRb are independently from each other hydrogen or lower alkyl;
R2 is aryl or heteroaryl, unsubstituted or substituted by lower alkyl or halogen; and
n is 0, 1, 2 or 3;
or a pharmaceutically acceptable salt thereof.
It has surprisingly been found that the compounds of formula I are adenosine receptor ligands.
Compounds of the present invention of formula I and their pharmaceutically acceptable salts are pharmaceutically active substances. The present invention includes a process for the manufacture of compounds of formula I and pharmaceutical compositions comprising a therapeutically effective amount of at least one compound of formula I and an excipient. The present invention is also directed to a method of controlling or preventing illnesses based on the modulation of the adenosine system, such as Alzheimer""s disease, Parkinson""s disease, neuroprotection, schizophrenia, anxiety, pain, respiration deficits, depression, asthma, allergic responses, hypoxia, ischaemia, seizure and substance abuse by administering a therapeutically effective amount of a compound of formula I to patient in need of such treatment. Furthermore, compounds of the present invention may be useful as sedatives, muscle relaxants, antipsychotics, antiepileptics, anticonvulsants and cardiaprotective agents. The most preferred indications in accordance with the present invention are those, which base on the A2A receptor antagonistic activity and which include disorders of the central nervous system, for example the treatment or prevention of certain depressive disorders, neuroprotection and Parkinson""s disease.
As used herein, the term xe2x80x9clower alkylxe2x80x9d denotes a saturated straight- or branched-chain alkyl group containing from 1 to 6 carbon atoms, for example, methyl, ethyl, propyl, isopropyl, n-butyl, i-butyl, 2-butyl, t-butyl and the like. Preferred lower alkyl groups are groups with 1-4 carbon atoms.
The term xe2x80x9ccycloalkylxe2x80x9d denotes a saturated carbocyclic group, containing 3-8 carbon atoms. A preferred cycloalkyl group is cyclohexyl.
The term xe2x80x9chalogenxe2x80x9d denotes chlorine, iodine, fluorine and bromine.
The term xe2x80x9clower alkoxyxe2x80x9d denotes a group wherein the alkyl residues is as defined above, and which is attached via an oxygen atom.
The term xe2x80x9carylxe2x80x9d denotes phenyl or naphthyl. The preferred aryl group is phenyl.
The term xe2x80x9cheteroarylxe2x80x9d denotes 5 or 6 membered rings with heteroatoms, such as O, N or S, for example, pyridinyl, thiophenyl, furanyl or thiazolyl.
The term xe2x80x9c5 or 6 membered non-aromatic ringxe2x80x9d denotes 5- or 6-membered rings, which may contain one additional heteroatom, such as O or S, in addition to the N atom, for example morpholinyl, thiomorpholinyl, piperidinyl, pyrrolidinyl or 3,6-dihydro-2H-pyridin-1-yl.
The term xe2x80x9cpharmaceutically acceptable acid addition saltsxe2x80x9d embraces salts with inorganic and organic acids, such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, citric acid, formic acid, fumaric acid, maleic acid, acetic acid, succinic acid, tartaric acid, methane-sulfonic acid, p-toluenesulfonic acid and the like.
A compound of formula I of the present invention, wherein R2 is heteroaryl, such as furan-2-yl, substituted by bromo, is preferred. A preferred compound of this embodiment is selected from the group consisting of:
[8-Amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-piperidin-1-yl-methanone,
[8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-methanone,
[8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-pyrrolidin-1-yl)-methanone,
1-[8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridine-6-carbonyl]-piperidine-3-carboxylic acid diethylamide,
[8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-(3,5-dimethyl-piperidin-1-yl)-methanone,
[8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-(2-methyl-piperidin-1-yl)-methanone,
[8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-(2-methoxymethyl-pyrrolidin-1-yl)-methanone,
[8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-((S)-2-methoxymethyl-pyrrolidin-1-yl)-methanone,
1-[8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridine-6-carbonyl]-pyrrolidine-2-carboxylic acid (S)-dimethylamide,
8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridine-6-carboxylic acid dimethylcarbamoylmethyl-methyl-amide,
[8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-(3-methyl-piperidin-1-yl)-methanone,
8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridine-6-carboxylic acid methyl-propyl-amide,
8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridine-6-carboxylic acid ethyl-(2-pyridin-2-yl-ethyl)-amide,
[8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-thiomorpholin-4-yl-methanone and
8-amino-2-(5-bromo-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridine-6-carboxylic acid methyl-phenethyl-amide.
A further preferred compound of formula I of the present invention is, wherein R2 is unsubstituted heteroaryl, such as furan-2-yl. An example of this preferred compound is selected from the group consisting of:
(8-Amino-2-furan-2-yl-[1,2,4]triazolo[1,5-a]pyridin-6-yl)-pyrrolidin-1-yl-methanone,
(8-amino-2-furan-2-yl-[1,2,4]triazolo[1,5-a]pyridin-6-yl)-(2-R-methoxymethyl-pyrrolidin-1-yl)-methanone,
(8-amino-2-furan-2-yl-[1,2,4]triazolo[1,5-a]pyridin-6-yl)-(2-S-methoxymethyl-pyrrolidin-1-yl)-methanone and
8-amino-2-furan-2-yl-[1,2,4]triazolo[1,5-a]pyridine-6-carboxylic acid dibenzylamide.
A compound of formula I of the present invention, wherein R2 is heteroaryl, such as thiophen-2-yl, is also preferred. Exemplary of this preferred compound is 8-Amino-2-thiophen-2-yl-[1,2,4]triazolo[1,5-a]pyridine-6-carboxylic acid dibenzylamide.
A further preferred compound is wherein R2 is heteroaryl, such as furan-2-yl, substituted by methyl. A compound exemplary of this preferred compound is selected from the group consisting of:
[8-Amino-2-(5-methyl-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-pyrrolidin-1-yl-methanone,
[8-amino-2-(5-methyl-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-piperidin-1-yl-methanone,
[8-amino-2-(5-methyl-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-(2-methyl-pyrrolidin-1-yl)-methanone and
8-amino-2-(5-methyl-furan-2-yl)-[1,2,4]triazolo[1,5-a]pyridine-6-carboxylic acid methyl-propyl-amide.
A compound of formula I of the present invention or a pharmaceutically acceptable salt thereof can be prepared by methods known in the art, for example, by processes described below, which process comprises reacting a compound of formula 
with an amine of formula
HNRxe2x80x2Rxe2x80x3xe2x80x83xe2x80x83III
to a compound of formula 
xe2x80x83wherein Rxe2x80x2, Rxe2x80x3 and R2 have the significance given above, and converting the compounds obtained into a pharmaceutically acceptable acid addition salt by reaction with a sufficient quantity of a pharmaceutically acceptable acid.
In accordance with the above mentioned process variant for obtaining a compound of formula I (8-amino-2-(aryl or heteroaryl)-[1,2,4]triazolo[1,5-a]pyridin-6-yl]-piperidin-1-yl-methanone), a solution of an amine of formula III (HNRxe2x80x2Rxe2x80x3) in dioxane is treated with trimethylaluminum in toluene and stirred for 1 h at room temperature. 8-Amino-2-(aryl or heteroaryl)-[1,2,4]triazolo[1,5-a]pyridine-6-carboxylic acid methyl ester (II) in 1 ml dioxane is added and the mixture is heated to 90xc2x0 C. for 72 h. HCl aq. is added and the volatiles are removed. The residue is taken up in 1 formic acid and methanol and purified by reversed phase preparative HPLC eluting with a gradient of acetonitrile and water.
Salt formation from a compound of formula I of the present invention is effected at room temperatures in accordance with methods familiar to a person skilled in the art. Pharmaceutically acceptable salts may be formed with pharmaceutically acceptable inorganic acids or organic acids. Hydrochlorides, hydrobromides, sulfates, nitrates, citrate, acetates, maleates, succinates, methane-sulfonates, p-toluenesulfonates and the like are examples of such salts.